1. Field of the Invention
The present invention relates to a projection type image display apparatus which projects a laser beam on a screen to display images.
2. Background Arts
A projection type image display apparatus, which modulates a laser beam with image data and projects the modulated laser beam on a screen to display images, is disclosed in, for instance, the Japanese patent laid-open publication No. 2000-267621. Since the laser beam has high energy, it may cause serious harm, such as burns, deterioration of eyesight or even blindness when a human body is directly irradiated with the laser beam.
The projection type image display apparatus disclosed in the Japanese patent laid-open publication No. 2000-267621 is a rear projection type to project the laser beam from the rear side of the screen. This projection type image display apparatus converts the laser beam emitted from a laser source into a broad beam by a lens and modulates the broad laser beam by a liquid crystal panel to project it on the screen. When the beam conversion is performed properly, the intensity of the laser beam becomes low and the optical energy is reduced. Therefore, it does not cause any harm even if the human body is irradiated with such laser beam, which has passed through the screen. However, if the intensity of the laser beam is maintained high due to fault in the beam conversion, the laser beam may be hazardous to the human body.
The projection type image display apparatus such as described above has a sensor disposed in a projection area of the laser beam on the screen for detecting the intensity of the laser beam being projected on the screen. When the intensity of the laser beam is high, the projection type image display apparatus stops outputting the laser beam or reduces the intensity of the laser beam.
In the rear projection type image display apparatus, the laser source including a laser optical system is placed in a case, and the screen is arranged in front of the case. The laser beam irradiated on the human body has already passed through the screen, therefore the energy of the laser beam is relatively low. In contrast to this, in a front projection type image display apparatus to project the laser beam from the front side of the screen, the laser beam emitted from the laser source can be directly irradiated on the human body, so it is dangerous. For this reason, countermeasures against the laser beam hazards to the human body are desired especially in the front projection type image display apparatus.